Good luck Cassini!

On Thu, 01 Jul 2004 04:15:00 GMT, Bruce Palmer
wrote:

Schweeeeet! Welcome to Saturn.

....and considering that my signature's one of those sent to Saturn on
Cassini, that's got a bit of a personal meaning to me as well!
Hoo-RAH!

OM

--

"No ******* ever won a war by dying for | http://www.io.com/~o_m
his country. He won it by making the other | Sergeant-At-Arms
poor dumb ******* die for his country." | Human O-Ring Society

- General George S. Patton, Jr

On Fri, 02 Jul 2004 06:15:01 GMT, Bruce Palmer
wrote:

Lockheed Martin did themselves proud last night, sir, I tip my cap to
you and your colleagues.

....I hoisted a few to both JPL and Lockmart this evening. The crowning
achievement to Tim and the guys at Lockmart is that only one of the
eight dancers who wanted to know why *I* who normally doesn't drink
when he's out and about was toasting something called "Cassini" had
AbZero clue what a "Cassini" was.

I was going to ask her if she had a clue whether Saturn has rings or
not, but I restrained myself knowing the obvious answer would have
resulted in a drink being poured over her head...

Success is never having to go to your backup engine!

....Take note, kids: This is a .sig that has to be stolen someday :-)

I can only imagine how you all and the JPL folks felt.

....Oh, I *know* how they felt this morning:

Flight: "Ok, all flight directors, let's go around the room for
go/nogo for SO1. NAV1?"

NAV1: "[groan] Not so loud, Flight. We're still hung over here..."

NAV2: "Flight? NAV2."

Flight: "Go NAV2."

NAV2: "What he said goes double for me, please."

Flight: "Sigh COMM?"

COMM: "Zzzzzz....."

I think everyone who's excited about the mission feels like a small part
of themselves is along for the ride. It's wonderful. I only found out
afterwards that Todd Barber, the commentator, was also a prop engineer.
That was very cool they let him do that.

....And he did a damn fine job with the commentary as well. Nowhere
near the dry attempts at quasihype that we've been "blessed" with on
certain Shuttle launches over the years.

Congrats on a job well done.

....Agreed. To be honest, I truly think on behalf of the regulars here
on ssh, Tim should feel free to pass on our compliments on the same to
everyone at JPL and Lockmart. This year's been one excellent one with
regards to unmanned space exploration, what with the MERs, Stardust,
MOST, SMART-1, and now Cassini. And the year's just barely half over,
too!

OM

--

"No ******* ever won a war by dying for | http://www.io.com/~o_m
his country. He won it by making the other | Sergeant-At-Arms
poor dumb ******* die for his country." | Human O-Ring Society

- General George S. Patton, Jr

In article ,
OM om@our_blessed_lady_mary_of_the_holy_NASA_researc h_facility.org wrote:
...This year's been one excellent one with
regards to unmanned space exploration, what with the MERs, Stardust,
MOST, SMART-1, and now Cassini...

And speaking of MOST, the first paper has indeed finally seen publication
in the 1 July Nature.

MOST spent, roughly, January staring at Procyon. It was a prime target
partly because there have already been some tentative observations of
oscillations using radial-velocity measurements from ground observatories.
And what MOST found when it looked for brightness oscillations was...
nothing! *No detectable oscillations at all.*

The hardware is working. The paper includes a nice plot of brightness
changes seen in a nearby star that happened to be within the field of view
and got designated as a secondary science target; it turns out to be
mildly variable on two different time scales. Procyon doesn't do anything
like that -- its curve just looks like a flat strip of noise at first
glance -- but when it's cranked through an analysis looking for dominant
frequencies, quite unexpectedly, nothing comes out.

Nobody knows what this means. Maybe the oscillations just aren't there.
Maybe they exist but are very short-lived, so they don't show up well.
Maybe the random noise in the brightness has different characteristics
than expected and it's swamping the oscillations. (Any of these means
that something is wrong with the Sun-based models used to predict the
observability of oscillations.) Maybe there is some subtle noise source
messing up the data (but what?).

As usual, the first look at the world using a new method came up with
results nobody expected...
--
"Think outside the box -- the box isn't our friend." | Henry Spencer
-- George Herbert |

(Henry Spencer) writes:

Nobody knows what this means. Maybe the oscillations just aren't there.
Maybe they exist but are very short-lived, so they don't show up well.
Maybe the random noise in the brightness has different characteristics
than expected and it's swamping the oscillations. (Any of these means
that something is wrong with the Sun-based models used to predict the
observability of oscillations.) Maybe there is some subtle noise source
messing up the data (but what?).

Have they tried looking at other stars with apparent magnitudes comparable
to Procyon but known oscillations, to make sure the instrument is working
properly for objects of Procyon's brightness?

--
pgf

In article ,
Phil Fraering pgf@AUTO wrote:
Nobody knows what this means...

Have they tried looking at other stars with apparent magnitudes comparable
to Procyon but known oscillations, to make sure the instrument is working
properly for objects of Procyon's brightness?

Trouble is, there *are* no stars with known oscillations on this sort of
time scale (except the Sun). These observations are almost impossible to
do from the ground. Procyon was, I gather, about the closest thing to a
"known oscillations" star available...

(You really want similar time scales etc., because the data analysis needs
verifying almost as much as the instrument does.)

MOST definitely has observed several other bright stars by now. (The one
major limitation of the small aperture, in fact, is that MOST works really
well only on relatively bright stars.) And verification will surely have
been high on the agenda after the Procyon results. We can hope that the
next paper won't take quite as long to appear...
--
"Think outside the box -- the box isn't our friend." | Henry Spencer
-- George Herbert |

(Henry Spencer) writes:

Trouble is, there *are* no stars with known oscillations on this sort of
time scale (except the Sun).

What freq/period is in question?
--
A host is a host from coast to
& no one will talk to a host that's close........[v].(301) 56-LINUX
Unless the host (that isn't close).........................pob 1433
is busy, hung or dead....................................20915-1433

In article ,
David Lesher wrote:
Trouble is, there *are* no stars with known oscillations on this sort of
time scale (except the Sun).

What freq/period is in question?

The region of greatest interest, I gather, is 0-5mHz (millihertz, not
megahertz), with the earlier reported detections based on radial velocity
generally around 1mHz (that is, a period of 10-20 minutes).
--
"Think outside the box -- the box isn't our friend." | Henry Spencer
-- George Herbert |

Phil Fraering pgf@AUTO wrote in message ...
(Henry Spencer) writes:

Nobody knows what this means. Maybe the oscillations just aren't there.
Maybe they exist but are very short-lived, so they don't show up well.
Maybe the random noise in the brightness has different characteristics
than expected and it's swamping the oscillations. (Any of these means
that something is wrong with the Sun-based models used to predict the
observability of oscillations.) Maybe there is some subtle noise source
messing up the data (but what?).

Have they tried looking at other stars with apparent magnitudes comparable
to Procyon but known oscillations, to make sure the instrument is working
properly for objects of Procyon's brightness?

Yes, eta Bootis. See the UBC press release at
http://www.astro.ubc.ca/MOST/milestones/June2004_2.html for some
details. Eta Boo is a solar-type star, slightly more massive than, and
younger than, our Sun. Solar-type oscillations were detected. (Quick
phone call to the PI...) Yup, this is the first detection of p-mode
oscillations in a Solar-type star (other than the Sun) based on
photometric measurements; it tends to confirm an earlier report of
p-mode oscillations based on spectroscopic observations.

From http://www.astro.ubc.ca/MOST/targetstars.html, Procyon is
magnitude 0.38, and eta Boo is magnitude 2.68. Those are relative
magnitudes as seen from Earth, through a broad-band visible-light
filter. I don't know their absolute magnitudes off-hand, but Procyon
is of spectral class F5V, and eta Boo is G0IV; based on OBAFGKMN, they
must be close in size...

So, this tends to confirm that the instrument is working as intended.
Stay tuned for more investigation into what the heck is going on with
Procyon...

- Kieran A. Carroll
Dynacon

Henry Spencer wrote:
Trouble is, there *are* no stars with known oscillations on this
sort of time scale (except the Sun). These observations are almost
impossible to do from the ground.

Were the observations of the Sun done from the ground?

Granted that the atmosphere makes stars twinkle, but that can be
factored out by comparing simultaneous data from multiple telescopes
distant from each other.

Procyon was, I gather, about the closest thing to a "known
oscillations" star available...

Were the oscillations observed from the ground at the same time as
they weren't observed from MOST? If not, perhaps Procyon has simply
temporarily stopped oscillating.

MOST definitely has observed several other bright stars by now.

It can only observe one at a time? If so, will it be rendered
obsolete by the upcoming Kepler mission?
--
Keith F. Lynch - http://keithlynch.net/
Please see http://keithlynch.net/email.html before emailing me.

In article ,
Keith F. Lynch wrote:
Trouble is, there *are* no stars with known oscillations on this
sort of time scale (except the Sun). These observations are almost
impossible to do from the ground.

Were the observations of the Sun done from the ground?

Some but not all. The Sun is a very different class of problem, because
(in particular) we can resolve its disk, and that makes other methods of
vibration detection available. And yes, there are space observations as
well as ground ones; SOHO in particular specializes in various kinds of
optical solar observations which can't be done from the ground.

Granted that the atmosphere makes stars twinkle, but that can be
factored out by comparing simultaneous data from multiple telescopes
distant from each other.

In principle, yes. In practice, it would take formidable resources to put
together a network that can do this well enough. To pull oscillations out
of normal surface noise, you need fairly continuous observations over a
period of weeks, meaning a worldwide network. (Regular interruptions in
the data -- e.g., a day/night cycle -- are absolutely deadly, injecting
large amounts of noise into the analysis results.) And really getting
the atmospheric scintillation completely out of the data is hard.

I believe people have tried, but nobody has succeeded, doing things that
way. The ground-based stellar detections have all used Doppler data
rather than brightness.

Procyon was, I gather, about the closest thing to a "known
oscillations" star available...

Were the oscillations observed from the ground at the same time as
they weren't observed from MOST? If not, perhaps Procyon has simply
temporarily stopped oscillating.

I don't *think* any of the ground observations were done at the same time.
But a temporary halt in oscillation is another one of those things that
would require revisions to the theories. The Sun doesn't do that.

MOST definitely has observed several other bright stars by now.

It can only observe one at a time? If so, will it be rendered
obsolete by the upcoming Kepler mission?

MOST is definitely a small "pathfinder" mission, with a number of
limitations. It's what could be done quickly on a very small budget, and
a larger and more capable (but much more expensive) satellite would
certainly make it obsolete. I'm not putting bets on which one it will be
until one actually makes it into space, but I'm sure it will happen within
a few years; there are two or three such projects in the works, and I
expect at least one will make it to completion without being canceled.

MOST's telescope has quite a narrow field of view, and it can only observe
a small patch of sky at any one time. Moreover, it can do *continuous*
observing only within a zone about 54deg wide, centered about 8deg above
the ecliptic, moving across the sky at about 1deg/day -- for continuous
observing, you have to be looking pretty much at right angles to the orbit
plane, so the Earth doesn't get in the way -- so you don't get to pick the
small patch arbitrarily.

And for high-precision brightness work, you want to spread the light out
over a number of pixels to avoid saturation and other problems; the
telescope has a small array of "lenslets" that do that, but that
effectively narrows the field of view still more, and adds spacing
constraints on any attempt to do multiple targets. The lenslets cover
only part of the field of view, so you can use the bare CCD for less
constrained observations, but the data won't be as good.

So in practice, you pretty much only get one primary target at a time
(there *has* already been some lower-precision observing of secondary
targets, interesting stars that happened to be in the field of view).

Spend a bunch more money on fancier optics, fancier detectors, and putting
the thing in a high orbit or a Lagrange point so the Earth doesn't get in
the way all the time, and you will definitely get a more flexible and
capable mission. Eventually. :-)
--
"Think outside the box -- the box isn't our friend." | Henry Spencer
-- George Herbert |